PARIS, Oct 18 (Reuters) - French energy group Engie said on Thursday it aims to restart four of its Belgian nuclear reactors by the end of the year, which will help ease a power supply crunch in the country.

Belgium is facing an unprecedented electricity supply crunch this winter as six of the country’s seven nuclear reactors - all operated by Engie - are offline due to concrete degradation and water cooling issues.

Engie supplies around 40 percent of Belgium’s industrial and residential power market.

Its deputy director general Pierre Mongin said the company has had to lease cocooned gas-fired plants, bring in heavy diesel generators and pay heavy industrial users to curb consumption so as to meet clients’ needs.

“We have arranged around 750 megawatts of additional capacity to meet the shortfall,” Mongin told journalists in Paris.

The power shortage has left Belgium scrambling to find additional power capacity for winter or face rationing and blackouts.

Mongin said Engie has recommended solutions to Belgium’s nuclear regulator FANC, and a timeframe to fix the concrete degradation at bunkers close to three reactor buildings and resolve the cooling issue at two other reactors.

A decision by the regulator is pending.

“By the end of the year, we should have three Doel reactors back online, and Tihange 1,” Mongin said.

He said Engie plans to restart the Doel 1 and 2 reactors, each with 433 megawatt (MW) capacity, as scheduled on around Dec. 10 and Dec. 30, by which time it would have resolved the issue with the water cooling systems.

The reactors have been offline since April and May respectively as part of a planned long-term overhaul, and would need permission from the regulator to restart.

“We expect that these would be resolved by those dates,” Mongin said.

Its Doel 3 reactor is currently online. Doel 4 is scheduled to resume production by Dec. 15, while Tihange 1, which went offline for maintenance and refuelling on Oct. 13 is expected back on Nov. 17. Tihange 2 and Tihange 3 are also offline and will not come back online until May and March 2019 respectively.

To fix the concrete degradation problem, the company has decided to build concrete roofs above the bunkers at a price tag of around 40 million euros ($46 million) each, he said, adding that it had proposed a remedial plan to the regulator.

“We cannot carry out the work while the reactors are running because, at any given time, there could be an unplanned outage which would release pressurised steam at 300 degrees Celsius,” he said. “This could be risky for workers, that is why we had to halt the reactors.” ($1 = 0.8703 euros) (Reporting by Bate Felix; Editing by Susan Fenton)